This invention relates to an auxiliary fuel supply device for an engine using alcohol as a main fuel.
Generally, in an alcohol engine using 100% alcohol such as methanol or ethanol as a fuel, or using alcohol which does not contain additives containing a low boiling point component, a cold start operation and a warm-up operation of the engine are greatly difficult owing to less inflammable characteristics of alcohol as compared with gasoline.
Namely, alcohol has a latent heat of vaporization greater than that of gasoline and a high inflammation point, and is composed of a single component exclusive of the low boiling point component. Therefore, there occurs difficulty in cold starting operation and warm-up operation in the alcohol engine.
To solve this problem, there has been proposed a device for supplying a small quantity of gasoline to an upstream side of a venturi portion of a carburetor. However, atomization of gasoline as the foreign fuel may not be sufficiently conducted. Further, a quantity of the gasoline to be supplied is smaller than that of the alcohol, resulting in unsufficient effect of fuel atomization.
To improve atomization, there has been proposed a device for supplying gasoline to a main well of the carburetor in a single system covering the cold starting operation and the warm-up operation of the engine. However, such a device may not cope with the fact that a quantity of an auxiliary fuel to be required upon cold starting is different from that upon warm-up. If the quantity of the auxiliary fuel to be required upon cold starting is set, the quantity of the auxiliary fuel to be supplied upon warm-up becomes uneconomically excessive.